本論文使用高介電係數材料氧化鉿（HfOx）薄膜作為絕緣層與十三烷基駢苯衍生物做為半導體層，探討半導體層成長在聚亞醯胺（Polyimide, PI, 型號為DA-9000）、聚甲基丙稀酸甲酯（Polymethylmethacrylate, PMMA）與交聯結合的poly（4-vinylohenol）PVP（C-PVP）等修飾層上對電晶體穩定度之影響。論文分為兩個部分：第一部分，研究不同鍍膜參數之氧化鉿薄膜，藉由改變氬氣與氧氣通量、濺鍍功率以及鍍膜時間，使氧化鉿薄膜達至最佳化，進而降低元件的操作電壓。當氬氣與氧氣通量越高以及濺鍍功率越低，其氧原子與鉿原子鍵結越完全、薄膜表面越疏水性且漏電流亦越低，而鍍膜時間主要影響為薄膜厚度以及電容值，雖然厚度越厚，漏電流越小，然而卻會犧牲其電容值，由材料分析以及電性分析可以得知當所通入的氬氣與氧氣比為40：20 sccm、鍍膜時間為120分鐘與鍍膜功率為120 W時為本實驗所有鍍膜參數中之最佳參數，故本實驗的元件皆以此參數濺鍍氧化鉿薄膜。
第二部分主要探討閘極汲極場效電壓、汲極場效電壓量測與連續電流對時間量測，而外加一長期的偏壓於電晶體，會使得累積在通道的電子被半導體與絕緣層介面或是靠近其介面的半導體晶界的深層能態所捕捉，而造成介面產生屏蔽效應以及金屬與半導體層之間的介面產生更多的缺陷，使得其接觸電阻增加，導致電晶體的臨界電壓越往正電壓偏移。然而本實驗室所使用的PI元件修飾層，卻是使電晶體的臨界電壓越變越小。由連續電流對時間量測曲線可觀察到，PTCDI-C13H27薄膜成長於HfOx、C-PVP與PMMA薄膜上，由於陷阱能態捕捉載子，使得電晶體的汲極電流大幅下降；然而成長於PI上的電晶體汲極電流卻是往上提升後才緩慢下降，使得電晶體在5000秒長期操作下時，汲極電流仍然高於初始的汲極電流，而PI修飾層所造成的元件臨界電壓和汲極電流上升的現象是目前文獻中皆未報導過的，故本實驗利用PI當修飾層成功的做出高穩定度的有機薄膜電晶體。

In this study, we have investigated the stability of low-voltage operated n-type organic thin film transistors (OTFTs). The OTFTs was used N,N'-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13H27) and hafnium dioxide (HfO2) as active layer and gate dielectric, respectively. The high-k HfO2 layer was deposited by radio-frequency (RF) sputtering, and then it was annealed at 200oC. All of devices have gate-dielectric modification layers, in which the modification materials, including polymethylmethacrylate (PMMA), Crosslinked-poly(4-vinylphenol) (C-PVP), and polyimide (PI, Daxin DA-9000), were spun onto the HfO2. This study was divided into two parts;
The aim of the first part is to deposit high quality HfO2 films using RF sputtering under various ratios of Ar and O2 gas-flows, sputtering powers, and sputtering times. Then, the composition and surface roughness of HfO2 films were examined by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). For investigating the electrical properties of the HfO2 films, the current-voltage and capacitance-voltage curves of metal-insulator-metal (MIM) structure were measured by the Keithley4200 semiconductor parameter analysis. The results show that the HfO2 films deposited at sputtering power of 100 W, gas-flow ratio of Ar : O2 = 40 : 20 sccm, and sputtering times of 120 minutes exhibit the optimum dielectric constant (k = 10) and the smallest leakage current in the MIM structure.
In the second part of this study, studies of time-dependent drain current (ID) continuously performed on devices with different polymeric buffer layers under VGS = VDS = 6 V for 5000 s. A modification-layer PI was spun onto the HfO2 surface to decrease the defects of HfO2 and to reduce the trap states between PTCDI-C13H27/ HfOx interface. Therefore, the OTFTs with the PI layer exhibited high electrical performances, including little hysteresis of threshold voltage and mobility. The time-dependent ID in the device with C-PVP and PMMA layer displayed degradation of 21% and 14%, respectively, at above stress condition due to the more carriers trapped in the polymer layer and semiconductor/polymer interface; hence, large threshold-voltage shift occurred in these OTFTs. In contrary, the time-dependent ID of device with the PI-modified HfO2 dielectric shows excellent stability at the same stress condition because the PI can reduce the trap state between semiconductor and gate-dielectric. Therefore, the device with the PI layer shows excellent performances and high stability when compared with device with C-PVP and PMMA polymer layers.

[1]M. Pope, H. Kallmann, and P. Magnante, “Electrolumi nescence in organic crystal”, J. Chem. Phys., 38, 2024 (1963) .
[2]C. K. Chiang, C. R. Fincher, Y. W. Park, A. J. Hegger, H.Shirakawa, E. J. Louis, S. C. Gua and A. G. MacDiarmid, “Electrical Conductivity in Doped Polyacetylene”, Phys. Rev. Lett., 39, 1098 (1977) .
[3]F. Ebisawa, T. Kurokawa, and S. Nara, “Electrical properties of polyacetylene/polysiloxane interface”, J. Appl. Phys., 54, 3255 (1983)
[4]F. Garnier, R. Hajlaoui, A. Yassar, and P. Srivastava, “All-Polymer Field-Effect Transistor Realized by Printing Techniques”, Science, 265, 1684 (1994).
[5]S. Lee, B. Koo, J. Shin, E. Lee, and H. Park, H. Kim, “Effects of hydroxyl groups in polymeric dielectrics on organic transistor performance”, Appl. Phys. Lett., 88, 162109 (2006) .
[6]M. C. J. M. Vissenberg, “Opto-Electronic Properties of Disordered Organic Semiconductors”, (1999).
[7]C. D. Dimitrakopoulos, and P. R. L. Malenfant, “Organic Thin Film Transistors for Large Area Electronics”, Adv. Mater., 14, 99 (2002)
[8]S. Kobayashi, T. Takenobu, S. Mori, A. Fujiwara, and Y. Iwasa, “C60 thin-film transistors with high field-effect mobility, fabricated by molecular beam deposition”, Adv. Mater., 4, 371 (2003)
[9]R. J. Chesterfield, J. C. McKeen, C. R. Newman, P. C. Ewbank, D. A. da S. Filho, J.-L. Brédas, L. L. Miller, K. R. Mann, and C. D. Frisbie, “Organic Thin Film Transistors Based on N-Alkyl Perylene Diimides：Charge Transport Kinetics as a Function of Gate Voltage and Temperature”, J. Phys. Chem. B, 108, 19281 (2004)
[10]S. Tatermichi, M. Ichikawa, T. Koyama, and Y. Taniguchi, “High mobility n-type thin-film transistors based on N, N’-ditridecyl perylene diimide with thermal treatments”, Appl. Phys. Lett., 89, 112108 (2006)
[11]T. D. Anthopoukos, B. Singh, N. Marjanovic, N. S. Sariciftci, A. M. Ramil, H. Sitter, M. Colle, and D. M. de Leeuw, “High performance n-channel organic field-effect transistors and ring oscillators based on C60 fullerene films”, Appl. Phys. Lett., 89, 213504 (2006)
[12]H. Klauk, U. Zschieschang, and J. Pflaum, M. Halik, “Ultralow-power organic complementary circuits”, Nature 445, 745 (2007)
[13]M. P. Walser, W. L. Kalb, T. Mathis, T. J. Brenner, and B. Batlogg, “Stable complementary inverters with organic field-effect transistor on Cytop fluoropolymer gate dielectric”, Appl. Phys. Lett., 94, 053303 (2009)
[14]J. Puigdollers, M. D. Pirriera, A. Marsal, A. Orpella, S. Cheylan, and C. Voz, R. Alcubilla, “N-type PTCDI–C13H27 thin-film transistors deposited at different substrate temperature”, Thin Solid Films, 517 (2009)
[15]A. Benor, A. Hoppe, V. Wagner, D. Knipp, “Electrical stability of pentacene thin film transistors”, Org. Electron, 8, 749 (2007)
[16]C. C. Kao, P. Lin, C. C. Lee, Y. K. Wang, J. C. Ho, and Y. Y. Shen, “High-performance bottom-contact devices based on an air-stable n-type organic semiconductor N, N-bis (4-trifluoromethoxybenzyl) – 1, 4, 5, 8 – naphthalene – tetracarboxylic di-imide”, Appl. Phys. Lett., 90, 212101 (2007)
[17]T. N. Ng, J. H. Daniel, S. Sambandan, A. C. Arias, M. L. Chabinyc, and R. A. Street, “Gate bias stress effects due to polymer dielectrics in organic thin-film transistors”, J. Appl. Phys., 103, 044506 (2008)
[18]H. W. Zan, and S. C. Kao, “The Effects of Drain-Bias on the Threshold Voltage Instability in Organic TFTs”, IEEE International Conference on EDSSC, 4760739 (2008)
[19]Y.R. Liua, J. L. YU, P. T. Laib, Z. X. Wanga, J. Hana, and R. Liaoa, “Threshold-voltage instability of polymer thin-film transistor under gate-bias and drain-bias stresses”, IEEE Electron Device Lett., 29, 155 (2008)
[20]G. D. Wilk, R. M. Wallace, and J. M. Anthony, “High-k gate dielectrics: Current status and materials properties considerations”, J. Appl. Phys., 89, 5243 (2001)
[21]K. J. Hubbard, and D. G. Schlom, “Thermodynamic stability of binary oxides in contact with silicon”, J. Mater. Res., 11, 2757 (1996)
[22]L. E. Alexander, “X-ray Diffraction Methods in polymer science”, Wiley, New York, p429 (1969)
[23]J. N. Israelachvili, “Intermolecular and surface forces 2nd edition”, Academic Press, London, UK, p83 (1992)
[24]C. R. Kagan, and P. Andry, “Thin-Film Transistors”, Marcel Dekker INC., p. 36 (2003)
[25]S.M. Sze, “Semiconductor Devices Physics and Technology 2nd edition”, John Wiley & Sons INC., p. 169 (2001).
[26]M. A. Lampert, “Simplified Theory of Space-Charge-Limited Currents in an Insulator with Traps”, Physical Review, 103, 1648 (1956)
[27]B. E. Deal, “Standardized terminology for oxide charges associated with thermally oxidized silicon”, IEEE Trans. Electron Dev., 27, 606 (1980)
[28]W. Y. Chou, C. W. Kuo, H. L. Cheng, Y. R. Chen, F. Y. Yang, D. Y. Shu, C. C. Liao, and F. C. Tang, “High Mobility Pentacene Thin-Film Transistors on Photopolymer Modified Dielectrics”, Jpn. J. Appl. Phys., 45, 7922 (2006)
[29]J. Aarik, A. Aidla, H. Mändar, T. Uustare, K. Kukli, and M. Schuisky, “Phase transformations in hafnium dioxide thin films grown by atomic layer deposition at high temperatures”, Appl. Surf. Sci., 173, 15 (2001)
[30]H. Kim, P. C. Mclntyre, and K. C. Saraswat, “Effect of crystallization on the electrical properties of ultrathin HfO2 dielectrics grown by atomic layer deposition”, Appl. Phys. Lett., 82, 106 (2003)
[31]鄭崇銘, “氧化鉿-氧化鈮閘極介電薄膜之特性研究”, 碩士論文, 國立成功大學 (2007)
[32]黃國瑋, “熱處理條件對氧化鉿與矽酸鉿薄膜特性的影響”, 碩士論文, 國立成功大學 (2008)
[33]W. Y. Chou, C. W. Kuo, H. L. Cheng, Y. R. Chen, F. C. Tang, F. Y. Yang, D. Y. Shu, and C. C. Liao, “The effect of surface free energy in gate dielectric for pentacene-based thin-film transistors”, Appl. Phys. Lett., 89, 112126 (2006)
[34]H. Kawaguchi, M. Taniguchi, and T. Kawai, “Control of threshold voltage and hysteresis in organic field-effect transistors”, Appl. Phys. Lett., 94, 093305 (2009)
[35]H. E. Katz, X. M. Hong, A. Dodabalapur, and R. Sarpeshkar, “Organic field-effect transistors with polarizable gate insulators”, J. Appl. Phys., 91, 1572 (2002)
[36]A. Salleo, and R. A. Street, “Kinetics of bias stress and bipolaron formation in polythiophene”, Phys. Rev. B, 70, 235324 (2004)
[37]T. H. Kim, C. G. Han, and C. K. Song, “Instability of threshold voltage under constant bias stress in pentacene thin film transistors employing polyvinylphenol gate dielectric”, Thin Solid Films,516,1232 (2008)
[38]H. Sakai, K. Konno, and H. Murata, “Tuning of threshold voltage of organic field-effect transistors by space charge polarization”, Appl. Phys. Lett., 94, 073304 (2009)
[39]A. Wang, L. Kymissis, V. Bulovic, and A. L. Akinwande, “Tunable threshold voltage and flatband voltage in pentacene field effect transistors”, Appl. Phys. Lett., 89, 112109 (2006)
[40]X. Hong, and B. Kippelen, “High-performance C60 n-channel organic field-effect transistors through optimization of interfaces”, J. Appl. Phys., 104, 104504 (2008)
[41]F. C. Chen, and C. H. Liao, “Improved air stability of n-channel organic thin-film transistors with surface modication on gate dielectrics”, Appl. Phys. Lett., 93, 103310 (2008)